1. Field of the Invention
The invention relates to an implantable catheter made of medically tolerated synthetic material, containing an elastic, plastically deformable polymer having a particularly high cold flow.
2. Discussion of the Background
U.S. Pat. No. 4,211,741 describes a coextruded medical-surgical tubing. The polyurethane layer (innen layer) creates a non-migrating medical-surgical inner surface, and the polyvinyl layer creates an inexpensive outer surface. The relative thickness of the two layers are selected to provide the desired characteristics, such as hardness, flexibility, coupler adaptability and the like.
DE-A-2,902,434 discloses a method for the deformation of vessel implants and for the preparation of tissue incorporation, in particular of umbilical cords. For the purpose of deformation, the umbilical cord is first dehydrated and then treated with an aldehyde. In order to facilitate the incorporation of the implant, the surface is roughened mechanically.
DE-A-3,239,318 deals with a formable polyurethane elastomer which has good blood tolerability and which is the product of reaction of an aliphatic organic diisocyanate, a polyether polyol of high molecular weight and 1,4-butanediol as a chain lengthener. By using two equivalents of diisocyanate per equivalent of the polyol of high molecular weight, an elastomeric material with a Shore A hardness of 70 is obtained. The polyurethane can be used for catheters.
In the DSG Report No. 17 of January 1984 (The Donalds Gilmore Laboratories) on Pellethane 2363, polyether/polyurethane resins which comply with the FDA requirements are described for medical purposes. The starting materials used are polytetramethylene ether glycol, 1,4-butanediol and diphenylmethane diisocyanate. The polyurethane can be made radiopaque by adding materials such as BaSO.sub.4. Despite the biological tolerability, express reference is made to the fact that, on account of the lack of long-term data, use for implants is not recommended.
The purpose of the known biologically tolerated substances was to produce continuously elastic, thermoplastic polymers which are dimensionally stable.
One disadvantage of known implantable catheters made of medically tolerated synthetic materials consists in the fact that their length in the implanted state is virtually constant. There are cases, however, when changes in the size of the body of the patient, for example growth, results in a failure of the implanted tube system or of the catheter, because the catheter does not grow too and the implanted lumen connection necessary for maintaining the body functions is broken. Thus, it is necessary, for example in the case of neonates or infants with disorders of the cerebrospinal fluid circulation in the cranial region, to drain excess fluid from the ventricle chamber system by means of a catheter, for example into the peritoneal cavity. Since disorders of this type cannot at present be rectified other than by implanting a catheter, the growth of the body with increasing age has the result that an implanted catheter becomes too short and the drainage or feeding of fluid from or, respectively, to certain areas of the body is impaired or interrupted. Since replacement of catheters which may be too short cannot in most cases be carried out in good time, the failure of the artificial lumen connections inside the body often has serious consequences on the patient's health.